1. Field of the Invention
The present invention relates generally to microelectronic device fabrication and, more particularly, the fabrication of a SAW device and/or a MEMS device having one or more conductive devices formed thereover.
2. Description of the Related Art
The following descriptions and examples are given as background information only.
Microelectronic devices have been developed for a diversity of applications using a variety of technologies. Some exemplary microelectronic devices include surface acoustic wave (SAW) devices and micro electromechanical system (MEMS) devices. SAW devices exploit the propagation properties of waves along the surface or the near surface of a substrate. Changes in velocity and/or amplitude of the waves correlate to physical parameters and, therefore, may be monitored to serve as a sensor. SAW devices are often used as bandpass filters in communication devices, such as mobile phone handsets and communication networks, for example. Other applications of SAW devices include but are not limited to torque sensors, pressure sensors, humidity sensors and temperature sensors. MEMS devices integrate electromechanical functions using mechanical moving structures formed upon wafers. MEMS devices are of interest in part because of their potential for providing miniaturized sensors and actuators and performing functions not done or poorly done by technologies including fixed structures formed upon semiconductor wafers. Examples of MEMS devices include but are not limited to switching devices used in optical telecommunications cables and sensing devices used to control the deployment of airbags in automobiles.
One challenge associated with both SAW and MEMS devices is that free areas are needed for the mechanical properties of the devices. Because of this restriction, other conductors and devices cannot be easily formed above SAW or MEMS devices. Consequently, SAW or MEMS devices are generally not integrated on the same chip with other conductive structures. Rather, additional conductors or circuits are generally formed external to the substrate upon which a SAW or MEMS device is fabricated and are often formed external to the device package. In cases in which additional conductors or circuits are fabricated on the same chip as SAW or MEMS devices, the additional devices must be laterally disposed across the chip, leading to undesirably large die sizes. Another predicament with SAW and MEMS devices is that the active regions of the devices can be very sensitive to the presence of surface contaminants. Surface contaminants may, for example, alter the wave velocities of a SAW device or modify the voltage level at which a moving part with a MEMS device is brought into contact or released from a contact pad. As a consequence, device performance may be degraded for the SAW device or MEMS device. Even a monolayer of contaminant on the surface of a SAW or MEMS device can noticeably alter device performance.
Accordingly, it would be beneficial to develop an architecture which includes a SAW and/or MEMS device integrally fabricated with one or more other conductive devices on a single substrate and which does not require an undesirably large die size. In addition, it would be advantageous to inhibit the formation of contaminants within the active region of the SAW or MEMS device during the formation of the architecture.